from RealClearPolitics:

Mitt Romney may be tight-lipped about his vice presidential short list, warning that only he and longtime aide Beth Myers know who is on it, but a close examination of the campaign’s activity suggests four contenders have risen through the ranks: Former Minnesota Gov. Tim Pawlenty, Ohio Sen. Rob Portman, Wisconsin Rep. Paul Ryan and Louisiana Gov. Bobby Jindal.

New Hampshire Sen. Kelly Ayotte and Virginia Gov. Bob McDonnell may be considered wild cards, and Romney has said he’s thoroughly vetting Florida Sen. Marco Rubio, though the first-term lawmaker’s status appears unchanged.

full article: http://www.realclearpolitics.com/articles/2012/07/05/romneys_vp_short_list_it_may_be_down_to_four_114698.html